Formation of images by inkjetting is employed in various fields of printing because this method is applicable to high-mix low-volume production. As one of image forming methods employing the inkjetting, there is a method in which a droplet of an inkjet ink caused to land on a substrate is cured with actinic radiation (hereinafter also referred to as the “actinic radiation-curable inkjet recording method”).
The actinic radiation-curable inkjet ink to be used for this recording method has been widely studied. For example, each of PTLs 1 to 3 describes an actinic radiation-curable inkjet ink containing a fluorescent brightener as a sensitizer to be used for improving the curability of an ink.
In recent years, an actinic radiation-curable inkjet ink that contains a gelling agent and undergoes sol-gel phase transition according to the temperature (hereinafter also simply referred to as the “gel ink”) has been developed. The gel ink is in a sol state when heated, and can be discharged through a nozzle of an inkjet head, and when the ink lands on a substrate after being discharged, it is cooled to undergo gelation, and thus, the gel ink has a characteristic of a high pinning property after landing. When the gel ink pinned on the surface of a substrate is irradiated with actinic radiation, the gel ink is cured on the surface of the substrate to form an image.
Various techniques for forming a desired image using a gel ink have been studied. For example, PTL 4 describes a method for controlling glossiness of an image by providing, on an image, a UV curable overcoat composition containing a gelling agent, a curable monomer, a curable wax, and a photopolymerization initiator if necessary. Besides, PTL 5 describes a curable ink having a characteristic to closely match glossiness of a printed region on a substrate with glossiness of an unprinted region.